Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 21050)
+++ wp-includes/post-template.php	(working copy)
@@ -501,7 +501,7 @@
 	if ( is_admin_bar_showing() )
 		$classes[] = 'admin-bar';
 
-	if ( get_background_color() || get_theme_mod( 'background_image' ) || get_theme_support( 'custom-background', 'default-image' ) )
+	if ( get_theme_mod( 'background_color' ) || get_background_image() )
 		$classes[] = 'custom-background';
 
 	$page = $wp_query->get( 'page' );
Index: wp-includes/class-wp-customize-manager.php
===================================================================
--- wp-includes/class-wp-customize-manager.php	(revision 21050)
+++ wp-includes/class-wp-customize-manager.php	(working copy)
@@ -337,7 +337,6 @@
 		$settings = array(
 			'values'  => array(),
 			'channel' => esc_js( $_POST['customize_messenger_channel'] ),
-			'backgroundImageHasDefault' => current_theme_supports( 'custom-background', 'default-image' ),
 		);
 
 		foreach ( $this->settings as $id => $setting ) {
Index: wp-includes/js/customize-preview.dev.js
===================================================================
--- wp-includes/js/customize-preview.dev.js	(revision 21050)
+++ wp-includes/js/customize-preview.dev.js	(working copy)
@@ -109,14 +109,13 @@
 				return;
 
 			update = function() {
-				var css = '',
-					hasDefault = api.settings.backgroundImageHasDefault;
+				var css = '';
 
 				// The body will support custom backgrounds if either
 				// the color or image are set.
 				//
 				// See get_body_class() in /wp-includes/post-template.php
-				body.toggleClass( 'custom-background', !! ( color() || image() || hasDefault ) );
+				body.toggleClass( 'custom-background', !! ( color() || image() ) );
 
 				if ( color() )
 					css += 'background-color: ' + color() + ';';
@@ -126,8 +125,6 @@
 					css += 'background-position: top ' + position_x() + ';';
 					css += 'background-repeat: ' + repeat() + ';';
 					css += 'background-position: top ' + attachment() + ';';
-				} else if ( hasDefault ) {
-					css += 'background-image: none;';
 				}
 
 				// Refresh the stylesheet by removing and recreating it.
Index: wp-includes/theme.php
===================================================================
--- wp-includes/theme.php	(revision 21050)
+++ wp-includes/theme.php	(working copy)
@@ -1109,7 +1109,7 @@
 	// A default has to be specified in style.css. It will not be printed here.
 	$color = get_theme_mod( 'background_color' );
 
-	if ( ! $background && ! $color && ! get_theme_support( 'custom-background', 'default-image' ) )
+	if ( ! $background && ! $color )
 		return;
 
 	$style = $color ? "background-color: #$color;" : '';
@@ -1133,10 +1133,6 @@
 		$attachment = " background-attachment: $attachment;";
 
 		$style .= $image . $repeat . $position . $attachment;
-	} elseif ( get_theme_support( 'custom-background', 'default-image' ) ) {
-		// If there is not a $background, but there is a default, then the default was
-		// removed and an empty value was saved. Remove it:
-		$style .= " background-image: none;";
 	}
 ?>
 <style type="text/css" id="custom-background-css">